We are engaged in improving the description and explanation of genetic variation in Man employing a combination of theoretical and experimental work. We are developing: a data bank, to be used for analyzing geographic patterns of genetic variation; new models of population structure; new types of gene frequency maps. We are also collecting historical and paleoanthropological information that is useful for interpreting the present picture of human variation. We have started experimental work of human population genetics aimed at the study of genetic polymorphisms by a technique of electrophoresis and after radioactive ligands have been added to blood. The introduction of this procedure has led to the detection of several new polymorphisms which require further investigation.